The present invention relates generally to magnetic disk drives and, more particularly, to active vibration cancellation within a disk drive using a multitude of accelerometers.
Magnetic disk drives generally read and write data on the surface of a rotating magnetic disk with a transducer or xe2x80x9cheadxe2x80x9d that is located at the far end of a moveable actuator. A servo control system uses servo control information recorded amongst the data, or on a separate disk, to controllably move the transducer from track to track (xe2x80x9cseekingxe2x80x9d) and to hold the transducer at a desired position (xe2x80x9ctrack followingxe2x80x9d). A detailed discussion of servo control systems is unnecessary because such systems are well known as set forth, for example, in patent application Ser. No. 09/138,841 that was filed on Aug. 24, 1998, entitled xe2x80x9cDISK DRIVE CAPABLE OF AUTONOMOUSLY EVALUATING AND ADAPTING THE FREQUENCY RESPONSE OF ITS SERVO CONTROL SYSTEM,xe2x80x9d and is commonly owned by the assignee of this application.
The industry has previously mounted various kinds of accelerometers on the disk drive in order to sense external forces.
One example is U.S. Pat. No. 5,426,545 entitled xe2x80x9cActive Disturbance Compensation System for Disk Drives.xe2x80x9d This patent discloses an angular acceleration sensor 22 that comprises an opposed pair of linear accelerometers 22a and 22b. The invention is intended for use with balanced actuator assembly 26. The overall sensor package 22 is mounted to the HDA 10 or drive housing, as shown in FIG. 1, in order to detect and correct for angular acceleration about the axis 27 of the balanced actuator assembly 26 that would otherwise produce a radial position error 30 (FIG. 2) due to the actuator""s inertial tendency to remain stationary in the presence of such acceleration.
U.S. Pat. No. 5,521,772 entitled xe2x80x9cDisk Drive with Acceleration Rate Sensingxe2x80x9d discloses a variation on that theme in that it uses an xe2x80x9cacceleration rate sensorxe2x80x9d 50 rather than a linear acceleration sensor (conventional accelerometer) or angular acceleration sensor. The sensor 50 is mounted to the disk drive housing 9.
U.S. Pat. No. 5,663,847 is yet another patent disclosing an angular accelerometer in a disk drive. It is entitled xe2x80x9cRejection of Disturbances on a Disk Drive by Use of an Accelerometer.xe2x80x9d In FIG. 1, the ""847 patent discloses an angular accelerometer 102 that is mounted to the drive""s base plate 104 in order to sense rotational motion 110. The ""847 patent is similar to the ""545 patent in that both are addressing the problem that when the disk drive containing a balanced actuator is bumped rotationally in the plane of the disk 112, a position error will arise because xe2x80x9cthe actuator 114 will retain its position in inertial space . . . xe2x80x9d (4:19-21).
PCT Application WO 97/02532 discloses another apparent use of an accelerometer that is described therein as a xe2x80x9cshock sensorxe2x80x9d 46 (See FIG. 3). This application is entitled xe2x80x9cDisk Drive Data Protection Systemxe2x80x9d. The WO 97/02532 application appears similar to the remainder of the presently known art in that it appears to disclose a single sensor that is mounted to the drive housing. According to the disclosure, the shock sensor 46 detects xe2x80x9cphysical shocks to the disk drive which may compromise data being transferred . . . xe2x80x9d
Conventional systems mount a single accelerometer to the overall disk drive and disable reading and/or writing when the output of the accelerometer surpasses a threshold. The ""545 patent discussed above is different in that it uses a angular acceleration sensor mounted to the overall disk drive to indicate when the drive is being shocked or vibrated about the pivot axis of a balanced actuator. However, it is only sensitive to rotational motion and it assumes that the actuator is a perfectly balanced actuator.
The foregoing uses of accelerometers are incapable of accurately detecting a motion of the head relative to the remainder of the disk drive and are subject, therefore, to an off-track condition due to acceleration of an imbalanced actuator. There remains a need, therefore, for a disk drive that detects the motion of the actuator relative to the disk drive and implements active vibration cancellation using a multitude of sensors.
The invention may be regarded as a disk drive comprising a head disk assembly 20 including a base 21, a rotating disk 23, and a rotary actuator 50 that pivots relative to the base; a first motion sensor 35 rigidly mounted relative to the base for sensing motion of the head disk assembly; and a second motion sensor 55 mounted to the rotary actuator for sensing motion of the rotary actuator relative to the motion of the head disk assembly. In a more particular embodiment, the first motion sensor is rigidly mounted relative to the base to output a first sense signal, the second motion sensor is mounted to the rotary actuator to output a second sense signal, and the disk drive further includes a means for controlling a disk function in response to a comparison of the first and second sense signals.
The invention may also be regarded as a method of controlling a disk drive having a head disk assembly 20 including a base 21, a rotating disk 23, and a rotary actuator 50 that pivots relative to the base, in order to achieve improved track following performance by reducing off-track error caused by shock and vibration, the method comprising the steps of: generating a first sense signal corresponding to a motion of the head disk assembly; generating a second sense signal corresponding to a motion of the rotary actuator relative to the motion of the head disk assembly; comparing the first and second sense signals in order to detect off-track movement of the rotary actuator while track-following; and compensating for the off-track movement. In a preferred embodiment of the method, the step of generating a first sense signal corresponding to a motion of the head disk assembly is accomplished by mounting a first motion sensor 35 rigidly relative to the base and the step of generating a second sense signal corresponding to a motion of the rotary actuator relative to the motion of the head disk assembly is accomplished by mounting a second motion sensor 55 to the rotary actuator that pivots relative to the base.